The present invention relates to a display system for the cockpit of an aircraft, in particular of a transport airplane.
It is known that, on airplanes, the data used in particular for flying, steering and navigation are presented to the crew primarily by means of two display systems: a control and display system (CDS) for nominal use and a standby navigation system (SNS) for emergencies, as set out below. For safety reasons, these two systems are independent from one another and different.
Conventionally, a CDS system is formed of different display units and supplies various data, in particular:                primary flight data (altitude, attitude, speed, etc.);        a (horizontal and vertical) navigation chart;        engine parameters;        the status of the aircraft;        the status of systems and dedicated warnings; and        various pages for determining and altering the flight plan, in order to manage communications with air traffic control and for supervisory purposes.        
In recent versions, some of the formats displayed by a CDS system have been interactive.
Moreover, there are attempts to integrate more and more functions into CDS formats, in relation to, for example:                navigation at an airport;        maintenance functions;        systems control;        communications via data transmission, etc.        
This has resulted in a significant increase in the total display surface area of the CDS system. At the same time, the size of each individual display unit of the CDS system is also increasing to allow the use of larger formats, such as airport maps. This has led to increases in the number of display units and the total display surface area.
Moreover, the SNS system can be used in particular (but not exclusively, as set out below) as a standby system in the event of a CDS system outage. The SNS system generally comprises:                a pitot probe and a static probe; and        one or more standby display units of the ISIS (or “integrated standby instrument system”) type, comprising a small display surface and inertial sensors (accelerometers and gyrometers).        
FR-2 784 457 relates to an ISIS standby display unit which displays piloting information (altitude, speed and attitude) for the aircraft on a screen.
The SNS system is formed so as to provide the functions which are essential for the crew to fly and steer the aircraft safely, until completion of the flight under way. The data displayed by an SNS system generally comprise:                air data and inertial reference (altitude, air speed, attitude, etc.) parameters; and        navigation information (crossings, etc.).        
While the current display solution based on the CDS and SNS systems are entirely satisfactory on existing aircraft, said systems might show some limitations for future aircraft, in particular for the following reasons.
The operational perimeter of the CDS system increases from one program to the next, supplying the crew with more information and doing so in a smarter manner: the data are thus filtered, processed and presented visually, so as to be easily interpretable by the crew, and this only when necessary.
As regards the operational perimeter of the SNS system, this remains stable. Thus, from an operational perspective, there is a widening difference between the CDS and SNS systems. For the crew, it may become more complicated in the future to manage the transition over to the SNS system after the outage of the CDS system. Indeed, even if future CDS systems make it possible to limit the training of the crew in many situations owing to an intuitive interface and new functions, the crucial aspect of a pilot's training will concern flying the aircraft using the basic SNS system. The SNS system is, therefore, a curb on the evolution of pilot training.
A simple solution would be to increase the operational perimeter of the SNS system. However, this is not possible without increasing the surface area allotted to said SNS system within the cockpit. Yet, space is already limited within the cockpit, and the SNS system needs to located within the pilots' visual field and correctly oriented. Moreover, it needs to be easy to transition between the SNS and CDS systems. The only possible arrangement which meets these requirements would be on the instrument panel. However, the entire instrument panel is already taken up by CDS systems and installing thereon a standby system which will not generally be used is not necessarily a satisfactory solution.